Control experiments varying stimulation voltage, frequency, and pulse width insured suprathreshold stimulation of neurons. Voltage imaging using the ArchWT-GFP archaerhodopsin-based voltage sensor54 confirmed that individual pulses (1 ms, 40 V, 83 Hz) reliably triggered single APs. The imaging and stimulation system was controlled by custom scripts written in MetaMorph software (version 7.7.5, Molecular Devices) and Ephus software55 (ephus.org). Detailed neuronal culture screening methods will be described elsewhere (T.J.W., T.W.C., E.R.S., R.A.K., V.J., L.L.L., K.S., and D.S.K., manuscript in preparation).
